A piezoelectric actuator converts electrical energy into mechanical energy by an electrostrictive effect element.
A conventional piezoelectric actuator includes an electrostrictive effect element having a laminated structure, a metal case housing the electrostrictive effect element therein, and a top cap and a bottom cap for covering top and bottom openings of the metal case, respectively. The structure of the electrostrictive effect element is described in the U.S. Pat. No. 4,681,667 issued on Jul. 21, 1987.
The top and bottom caps are shaped to have hollow portions at the center thereof to set ends of the electrostrictive effect element therein, respectively. The metal case is shaped to have wavy surface to be expandable and contractible in a longitudinal direction such as a bellows.
In the conventional piezoelectric actuator, when a predetermine voltage is applied to the electrostrictive effect element, electrostriction is generated therein, so that the piezoelectric actuator expands and contracts to function as a mechanical driving source for a massflow controller, an X-Y table, an injection molding apparatus, etc.
However, the conventional piezoelectric actuator has a disadvantage in that it is difficult to provide an axis alignment between the electrostrictive effect element and each of the top and bottom caps, because the electrostrictive effect element is engaged at the both ends with recesses having predetermined clearances provided on the top and bottom caps, so that shearing stress occurs in the electrostrictive effect element, when the piezoelectric actuator is driven. Therefore, the electrostrictive effect element is broken by the shearing stress.